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Table of Contents    
Year : 2014  |  Volume : 62  |  Issue : 3  |  Page : 336-338

"Boomerang sign" in rickettsial encephalitis

Departments of Neurology, St. John's Medical College Hospital, Bangalore, Karnataka, India

Date of Web Publication18-Jul-2014

Correspondence Address:
Thomas Mathew
Department of Neurology, St. John's Medical College Hospital, Sarjapur Road, Bangalore - 560 034, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0028-3886.137030

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How to cite this article:
Mathew T, Badachi S, Sarma G, Nadig R. "Boomerang sign" in rickettsial encephalitis. Neurol India 2014;62:336-8

How to cite this URL:
Mathew T, Badachi S, Sarma G, Nadig R. "Boomerang sign" in rickettsial encephalitis. Neurol India [serial online] 2014 [cited 2021 Jan 24];62:336-8. Available from:


Transient signal alteration in the splenium of corpus callosum on magnetic resonance imaging (MRI) has been reported in a variety of neurologic and non-neurologic conditions. [1] We report a case of rickettsial encephalitis with transient splenial hyperintensity (TSH) in the splenium of corpus callosum, appearing like a boomerang on MRI.

A 17-year-old male had high-grade fever for five days. On day 5 of fever, he developed maculopapular pruritic rashes all over the body including palms and soles. Later he developed frontal headache, nausea and vomiting followed by altered sensorium. There was mild enlargement of liver and spleen. Neurological examination revealed a drowsy patient with neck stiffness and left oculomotor palsy. Cerebrospinal fluid showed ten lymphocytes and elevated proteins with normal sugars. Blood tests for malaria, dengue and leptospirosis were negative. Weil-Felix reaction showed rising titers for Ox-K antigen. MRI brain diffusion weighted image (DWI) showed lesions with restricted diffusion in the splenium and genu of the corpus callosum [Figure 1]. On apparent diffusion coefficient (ADC) mapping, these lesions had low apparent diffusion coefficient [Figure 2]. Magnetic resonance imaging-fluid-attenuated inversion recovery/T2w (MRI FLAIR/T2w) imaging showed hyperintense lesions in the splenium of corpus callosum [Figure 3]. However, the hyperintensity was less prominent in these sequences when compared to DWI and ADC images. The lesion was hypointense on T1w image [Figure 4] and did not show any enhancement on contrast administration [Figure 5]. The splenial lesion mimicked a boomerang. Patient improved completely with doxycycline and a short course of steroids.

The TSH has been reported in a variety of conditions, including infections, demyelination, ischemia and metabolic abnormalities [Table 1]. Infectious etiology for TSH can be viral, bacterial, spirochetal or mycobacterial. [2] Rickettsial encephalitis as a cause of TSH has not been reported in literature. TSH can be seen in two distinct patterns, either as a well-circumscribed, small, oval lesion in the midline within the substance of the corpus callosum or as a more extensive ill-defined irregular lesion extending throughout the splenium and into the adjacent hemispheres. In our patient, MRI Brain showed involvement of both anterior and posterior regions of corpus callosum. Posterior (Splenial) lesion mimicked a boomerang.
Figure 1: MRI diffusion weighted imaging showing splenial hyperintensity (boomerang sign- long black arrow) and hyperintensity in the genu of corpus callosum (short black arrow)

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Figure 2: ADC map showing signifi cant restricted diffusion with reduced ADC values in the splenium of corpus callosum (Long white arrow) and genu of corpus callosum (short white arrow)

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Figure 3: MRI brain FLAIR image showing hyperintense white matter lesion in the splenium of corpus callosum as compared with the hypointense white matter in the frontal region (white arrow)

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Figure 4: MRI brain T1w image showing hypointense lesion in the splenium of corpus callosum (long white arrow) and genu of corpus callosum (short white arrow)

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Figure 5: MRI brain with contrast did not reveal any enhancement of the splenial lesion

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Corpus callosum is the largest commissural pathway consisting of a cross-sectional area representing twice the magnitude of the sum of all the other commissural structures in the brain of an adult. It consists of myelinated axons that cross the midline in the developing brain in order to connect homologous regions of the two hemispheres. Major portion of the corpus callosum receives its arterial supply from the carotid system except for splenium, which is supplied by the vertebrobasilar system. [3] The exact mechanism for the development of TSH is not known. The proposed mechanisms implicated include, a transient breakdown of the blood-brain barrier, extrapontine osmotic myelinolysis due to sodium and glucose imbalance, intramyelinic edema due to inflammation and migration of inflammatory cells, cytokine-mediated immunologic reaction leading to microvascular endothelial injury, direct viral invasion of neurons and toxicity or hypersensitivity to antiepileptic drugs (AEDs). [4]
Table 1: Differential diagnoses of transient splenial hyperintensity

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The clinical significance of this sign is not certain and may denote a non-specific brain injury. The pattern of splenial hyperintensity does not indicate the etiology. Both boomerang and dot signs have been described in patients with encephalitis. However, it is interesting to note that most of the SCC lesions in patients with epilepsy were ovoid or round in shape. [5] TSH is an isolated, silent, reversible lesion and should not be mistaken for something more sinister. These are usually asymptomatic and do not produce features of disconnection syndromes, like apraxia. They are fully reversible and disappear after few weeks. The exact reason for increased predilection of the splenium of corpus callosum is still unclear and needs further animal and human research.

 » References Top

1.Doherty MJ, Jayadev S, Watson NF, Konchada RS, Hallam DK. Clinical implications of splenium magnetic resonance imaging signal changes. Arch Neurol 2005;62:433-7.  Back to cited text no. 1
2.Malhotra HS, Garg RK, Vidhate MR, Sharma PK. Boomerang sign: Clinical significance of transient lesion in splenium of corpus callosum. Ann Indian Acad Neurol 2012;15:151-7.  Back to cited text no. 2
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3.Tada H, Takanashi J, Barkovich AJ, Oba H, Maeda M, Tsukahara H, et al. Clinically mild encephalitis/encephalopathy with a reversible splenial lesion. Neurology 2004;63:1854-8.  Back to cited text no. 3
4.Bulakbasi N, Kocaoglu M, Tayfun C, Ucoz T. Transient splenial lesion of the corpus callosum in clinically mild influenza-associated encephalitis/encephalopathy. Am J Neuroradiol 2006;27:1983-6.  Back to cited text no. 4
5.Takanashi J, Barkovich AJ, Shiihara T, Tada H, Kawatani M, Tsukahara H, et al. Widening spectrum of reversible splenial lesion with transiently reduced diffusion. Am J Neuroradiol 2006;27:836-8.  Back to cited text no. 5


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1]

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